diff --git a/Geo/GModelIO_CELUM.cpp b/Geo/GModelIO_CELUM.cpp
index 38b7263cc20574cae05ab0788699c7cd106887aa..c20b4b5bc9371da74edd88807dbd6ed8f7e670dc 100644
--- a/Geo/GModelIO_CELUM.cpp
+++ b/Geo/GModelIO_CELUM.cpp
@@ -31,6 +31,8 @@ int GModel::writeCELUM(const std::string &name, bool saveAll,
     return 0;
   }
 
+  if(noPhysicalGroups()) saveAll = true;
+
   // count faces and vertices; the CELUM format duplicates vertices on the
   // boundary of CAD patches
   int numf = 0, nums = 0;